 This is going to be a demonstration of the flat muscles of the abdomen. So this is the supine cadaver. These are the left side. Most of the abdominal muscles have been removed and the contents have been removed. So we are going to demonstrate whatever is visible of the flat muscles on the lateral aspect of the left side. This muscle which I picked up here, this is the external oblique muscle of the abdomen. The external oblique muscle as we can see the national fibers are as if the hands and the pocket downwards and anteriorly. As the fibers come down they become aponeurotic. So this is the aponeurosis of the external oblique muscle of the abdomen. These fibers they take origin from the fifth to the twelfth ribs and as they come anteriorly they get inserted onto the outer lip of the iliac crest which is being traced by my finger here and then after that from the anterior supia iliac spine to the pubic tubercle. The aponeurosis gets attached and it forms a free margin and this free margin of the aponeurosis constitutes what is known as the inguinal ligament and if you look closely there's a space under the inguinal ligament which is called the sub-inguinal space my finger has gone in from where contents from the abdomen come out into the thigh. So this is the external oblique muscle. This muscle was covered by a thin layer of fascia which we have removed and the remnant of the fascia can be visible here. Now I'm going to reflect this and then we see the next muscle. This is the internal oblique muscle of the abdomen. This takes origin on the middle lip of the iliac crest and it also takes origin as we can see here from the lateral half of the inguinal ligament itself and the fibers then get inserted onto the linear alba which I'm going to describe a little later and they also get inserted onto the tenth and the eleventh and twelfth ribs. If you take a look at the dash of the fibers of the internal oblique we notice that the dash of fibers are at right angles to that of the external oblique. This is as if the hands are crossed over to the opposite chest. Then we have the third layer of muscle. This is the transversus abdominisis muscle and we can see that the dash of fibers are almost transverse that's why they are called transversus abdominisis. This takes origin from the seventh to the twelfth ribs and from the inner lip of the iliac crest also takes origin from the lateral one-fourth of the inguinal ligament. The medial fibers then they become aponeurotic and then they merge with the fibers aponeurosis of the internal oblique and transversus abdominisis and they form the rectus sheath and the linear alba. The rectus sheath is a tough sheath here which covers the rectus muscle. This is the anterior layer of rectus sheath on the left side which I'm holding up here and we can see that it is formed by the fused aponeurosis of the external oblique and partly by the anterior layer of the aponeurosis of the internal oblique and my finger has gone between the two fused layers. I'm holding up the left part of the anterior rectus sheath. We can see the same thing on this side also. This is the rectus sheath on the right side of the abdomen which is also formed the same way. The posterior layer of rectus sheath gets covering from posterior half of the internal oblique aponeurosis and the transversus abdominis aponeurosis. So that is how the medial portion of these three muscles aponeurotic portions form. Having mentioned the rectus sheath now let us show which muscle they are covering. This is the rectus abdominis muscle most of which we have cut only the lower portion is remaining. So this is the left rectus abdominis muscle this is the right rectus abdominis muscle. The rectus abdominis muscle takes attachment from the pubic symphysis pubic crest pubic tubercle on each side and as it climbs up it becomes wider and it gets attached to fifth sixth and seventh costal cartilages. So this is the full extent of the rectus abdominis muscle. When we lift up the rectus we notice a vascular structure which is running on the inner surface of the rectus. This is the inferior epigastric artery and the inferior epigastric vein. So let's trace the vascular structure on the left side. We can see it is coming out from the left external iliac artery and external iliac vein. So therefore this is the left inferior epigastric artery and the vein. Similarly on the right side we can see they are coming from the right external iliac artery and external iliac vein. This inferior epigastric vessels they enter into the rectus sheath through the arcuate line and then they run on the posterior surface of the rectus abdominis muscle up within the posterior of rectus sheath which of course is not visible here and they anastomose with a branch from this artery here which I'll show you on the inner surface of the chest wall. We can see the internal thoracic artery running on both the sides. This internal thoracic artery at the level of the seventh rib divides into a muscular pharynx and a superior epigastric on each side. This superior epigastric pierces through the anterior lateral gap of the diaphragm and this anastomosis with the inferior epigastric artery. The communication between the vein, the inferior epigastric vein and the superior epigastric vein constitutes an important communication between the superior vena kiva and the inferior vena kiva. And thereafter in the midline there is a structure called the linear alba which I'm going to show you by bringing the chest wall in front of us. So I brought the chest wall here and we can see the linear alba is attached to it. This is the place where the fibres from one side criss-cross with the fibres of the opposite side and if you were to take a very close look we can see the criss-crossing fibres. In the linear alba the deep fibres of the external oblique from one side criss-cross with the superficial fibres of the external oblique of the opposite side and vice versa and at the same time the fibres of the external oblique criss-cross with the fibres of the internal oblique of the opposite side and vice versa. And that is why these criss-crossing fibres constitute this tough aponeurotic sheet in the midline which is referred to as the linear alba which constitutes one strong component of the anti-abdominal wall. The next structure which I would like to draw your attention to in the anti-abdominal wall is this which I have lifted up here. This outer portion that we see here, this is the fascia transversalis and we can see it is slightly rough. This was the one which is lining the inner surface of the flat muscles of the abdomen and the inner portion that we see here is shiny and smooth. This is the parietal peritoneum and in between the two layers will be a little bit of variable amount of fat which is referred to as extra peritoneal fat though it is not present in this particular cadaver and that is located in a space called the space of bog rows. What are the nerve supply of these muscles? These muscles are supplied by the thoracoabdominal nerves. I have picked up this nerve here. This is the 12th subcostal nerve because it is arising from under the 12th rib. And above that we have the thoracoabdominal nerves which is from 7th to the 11th. They all come from the thoracic region and then they come and they supply the abdominal flat muscles. Additionally, the internal oblique muscle and the transverse abdominis muscle also take its nerve supply from this nerve here. This is L1. This divides into iliohypogastric and ilioinguinal and these iliohypogastric and ilioinguinal apart from supplying the skin of the lower abdomen and the thigh and other regions they also supply the internal oblique and the transverse abdominis. That brings me to the function of these fat muscles apart from forming the rectus sheath and the linear alba. They help to contain the intraabdominal organs that is the most basic function. They also help to increase the intraabdominal pressure when it is required like for example during coughing, sneezing or defecation. They are also responsible for lateral torsion of the trunk of the opposite side. So muscles of this side will cause torsion of that side and vice versa. So these are some functions of the flat muscles of the abdomen. One quick word about the inferior free margin of the external oblique aponeurosis which I had mentioned was the inguinal ligament. It extends from the anterior superioria spine to the pubic tubercle. Upturned portion of the inguinal ligament is where my finger has gone in. This forms the floor of the inguinal canal. External oblique muscle aponeurosis forms the anterior wall of the inguinal canal. Internal oblique and the transverse abdominis fibres which converge here to form what is known as the conjoined tendon. They form part of the roof and part of the posterior wall of the inguinal canal. So that is also another function of these flat muscles of the abdomen. However, inguinal canal is more prominent in males because that is the site where the intestines descends down but this is a female cadaver. So therefore the inguinal canal is not very prominent. These were some of the points which I want to mention to you about these flat muscles of the abdomen. Thank you very much for watching. Dr. Sanjay Sanyal signing out. David Oval is the camera person. If you have any questions or comments please put them in the comment section below. Have a nice day.